Various different types of hydrocarbon exploration systems can be used to determine whether a subterranean structure includes a reservoir that contains hydrocarbons. One type of hydrocarbon exploration system is a cross-well exploration system that includes a first tool having a survey source provided in a first well, and a second tool having a survey receiver (or array of survey receivers) provided in a second well. With this cross-well arrangement, the survey source in the first well is activated to transmit signals that are propagated through a subterranean structure between the first and second wells for receipt by the survey receiver (or array of survey receivers) in the second well.
Another type of hydrocarbon exploration system is a surface exploration system in which survey sources and receivers are placed on or above a surface over the subterranean structure of interest. Signals from the survey sources are propagated into the subterranean structure, with subterranean elements (including any reservoirs that may be present) reflecting signals back up to the surface for detection by the survey receivers.
Examples of survey sources and receivers include seismic sources and receivers or electromagnetic (EM) sources and receivers.
An issue associated with hydrocarbon exploration systems is synchronization of different tool components that may be spaced apart by relatively large distances. In many cases, it may be desirable to synchronize events occurring in multiple tool components placed in different locations. Some conventional systems relied upon a surface free-running reference clock and a cable connection from the reference clock to a remote tool component, where a reference clock signal is transmitted through the cable to the remote tool component. This approach made the assumption that the propagation delay through the cable between the reference clock and the remote tool component remains constant, regardless of temperature, pressure, or mechanical changes. Any change in the cable delay (drift) can introduce an unknown error in the measurement. In fact, over long distances, the delay over the cable can be quite large (e.g., tens of microseconds). Such a conventional approach does not enable accurate synchronization of events occurring at multiple tools. In addition, the repeatability between time-lapsed surveys made with a conventional technique relies on using the same cable or cable with equivalent delay each time a survey is made, which is impractical in field operations.